1. Field of the Invention
The invention relates to the manufacture of laminated components. More particularly, the present invention relates to a method of manufacturing laminated optical components by the replication of a light shaping surface structure on a rigid substrate. The invention additionally relates to an apparatus for performing this method.
2. Discussion of the Related Art
Methods of replicating optical components on substrates to achieve final products having desired surface characteristics are well known. Final products include viewing screens and homogenizers and are each characterized by a light shaping surface structure on at least one surface thereof. These products are made by 1) generating a surface structure on a photosensitive medium using coherent light, 2) processing the medium, and 3) replicating the surface structure in epoxy. Due to shrinkage of the photosensitive material at different stages of processing, at least one and usually several generations of submasters, made in sequence, are usually required to produce an optical product having the desired optical characteristics. In the final stage, a reusable submaster containing the desired surface structure is pressed against a substrate that has been coated with a layer of liquid epoxy. The liquid epoxy is then cured and the submaster is removed from the substrate/cured epoxy laminate. Depending upon the application, the substrate may comprise either a flexible thin film or a thick and relatively rigid substrate such a polycarbonate, glass, or acrylic. The invention is concerned with replicating surface structures on rigid substrates of this type.
Surface structures were heretofore replicated on rigid substrates either manually or semi-automatically. Both of these processes exhibit distinct drawbacks and disadvantages.
The manual process comprises four steps. First, a substrate is laid on a rigid, flat surface, and a layer of epoxy is dispensed onto the substrate. Then, a flexible plastic submaster is laid on top of the substrate to sandwich the epoxy layer between the substrate and the submaster to form a layered structure. The submaster contains the surface structure of interest on a surface thereof which faces the substrate. Then, a neoprene-coated roller or rubber-coated roller is manually rolled over the layered structure so that the layered structure is compressed through a line-to-surface contact caused by interaction of the roller and the flat surface. This compression replicates the surface structure of interest in the epoxy layer. The epoxy is then cured via exposure to ultraviolet (UV) light to form a laminated substrate covered with the submaster. Finally, the submaster is manually peeled from the laminated substrate.
The manual replication process is very laborious and time consuming, with the typical production rate ranging from five-to-ten units per hour, depending upon the complexity of the replicated surface structure. In addition, it is very difficult to assure uniform pressure application during the pressing process. This is problematic because uneven pressure application may result in inconsistencies in the finished product. These problems may be compounded if a non-uniform layer of epoxy is deposited onto the substrate prior to the laying down of the submaster onto the substrate and the subsequent pressing operation.
The semi-automatic process uses a machine known as a laminator to compress the layered substrate/epoxy/submaster structure. The laminator comprises first and second nip rolls which are driven in opposite directions to pull the layered structure through a nip formed between the first and second nip rolls. The first nip roll is driven by a DC electric motor or the like, and the second nip roll is driven by way of meshing contact between a driven gear on the second nip roll and a drive gear on the first nip roll. The layered structure is compressed as it is pulled through the nip. The operator then 1) exposes the compressed layered structure to UV light to cure the epoxy and to form a laminated substrate and 2) manually peels the submaster from the laminated substrate in the same manner as in the manual process.
While the semi-automatic process is marginally faster than the manual process, it does not necessarily produce a better-quality product for several reasons. First, because the layered structure experiences line-to-line contact in the nip rather than the line-to-surface contact experienced during the manual process, the layered structure tends to teeter or rock about the nip rolls as the operator feeds the structure through the nip. Unevenness in pressure application therefore can result. Second, speed differentials tend to exist between the two nip rolls due to backlash in the gearing coupling the nip rolls to one another. These speed differentials can result in slippage between the two surfaces of the pressed layered structure during the compressing operation. This slippage further degrades the quality of the finished product. In addition, excess liquid epoxy is often squeezed out of the layered structure during the compressing process and must be wiped off before the submaster is peeled from the substrate. This liquid epoxy may seep between the submaster and the substrate while the compressed layered structure is being transferred to the UV source, thereby damaging the product.
The need therefore exists to provide a machine that can 1) relieve the tedium and slow production rate of a manual replication process and 2) assure a good-quality product by uniformly pressing a submaster and substrate together with little or no slippage therebetween.